Only the IRS controls the timing of those, and is validating all claims for a Recovery Rebate Credit for stimulus #1 and #2. Also see:
IRS letters explain why some 2020 Recovery Rebate Credits are different than expected | Internal Rev...
The IRS is sending out Stimulus #3 payments in batches, and will take a few weeks to complete them all. This one comes to you separately (and automatically), not as part of your 2020 tax refund. You can check the status here:
Get My Payment | Internal Revenue Service (irs.gov)
